Wheel bearing seals used between an automotive wheel hub and shaft to retain and protect a lubricant supply from the ambient are generally garter spring seals. The typical garter spring seal includes a metal case that is press fitted into a bore in the hub, with an elastomer seal molded to the case has a seal lip that directly contacts the outer surface of the shaft. A garter spring surrounding the lip maintains its sealing force on the shaft and compensates for irregularities in and wear of the shaft surface.
Although they provide an effective seal, sprung seals create a great deal of rubbing friction, generally referred to as seal torque. A response to the high seal torque problem is disclosed in U.S. Pat. No. 4,497,495, assigned to the assignee of the present invention. The general type of seal disclosed there is known as unitized seal assembly. A unitized seal assembly has a pair of metal casings, one that press fits to each of the two bearing members. One of the casings provides the seal contact surface, rather than the outside of the shaft. Ideally, the two casings are retained together as a unit before installation for easy handling. A unitized seal assembly may also use a garter spring, which, of course, would still involve high seal torque. However, the seal in the above patent reduces seal torque very significantly by using a pair of unsprung seal lips molded to one casing which make a closely controlled, relatively light sealing contact with the other casing. The seal lips are stationary, so as to avoid centrifugal effects, and are oriented in such a way as to actually allow pressurized lubricant to exit, while preventing the ingress of contaminants. While it has proved highly successful, such a seal would not be practical in an environment where the anticipated pressure or other conditions could cause the loss of significant amounts of lubricant. There is, therefore, a need for a unitized seal assembly of comparably low seal torque that also has a better capacity to prevent the loss of significant amounts of lubricant in such an environment.